Continuity mistake: When Sam sits down next to Carol Twilling on the bed, asking, "Do things ever get a bit frisky?" the top button of his shirt is undone. The camera cuts away and back, only to find that there are now miraculously two buttons undone, not just one. Sam has not moved in this time.
Continuity mistake: During the scene between Hunt and Tyler, which takes place directly after Hunt has been "communicating" his outrage to Dickie Fingers, by hitting Dickie's hand repeatedly with a telephone, Hunt puts his hands in his pockets. However, in the next shot, which is the opposite camera angle, Hunt's hands are suddenly back out of his pockets. When the camera angle changes again, they're back in, all with no movement on Gene Hunt's part.
Factual error: Sam's watch (which we see when he checks it just after the escape attempt) is a quartz movement "analog" with a little window at the bottom where an LCD (Liquid Crystal Display) display shows the date. LCD didn't appear on watches or calculators for another five or six years.(Although in 1973, there were Digital Watches with LED (Light Emitting Diode) displays. (You can see Roger Moore as James Bond wearing one in "Live and Let Die"(1973)).
Factual error: Sam and Gene arrive at a construction site to investigate stolen explosives. There is a green first generation Range Rover parked on the site. The Range Rover has its driver side (right side) side view mirror mounted on the door. In 1973 Range Rovers had side view mirrors mounted on the front end of the front wing (fender), not the door. The mirror was not mounted to the door until after 1978. (00:08:58)